Connection for the operation of high frequency amplification systems



May I, 1934. w scHAF R 1,956,964

CONNECTION FOR THE OPERATION OF HIGH FREQUENCY AMPLIFICATION SYSTEMS Original Filed Nov. ll, 1926 RFSISMIVCT Z3 INVENTQR WALTER SCH'AFFER TORNEY Patented May 1, 1934 UNITED STATES PATENT OFFICE CONNECTION FOR THE OPERATION OF FREQUENCY AMPLIFICATION SYS- S Walter Schiiffer, Berlin, Germany, assignor to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application November 11, 1926, Serial No. 147,676. Renewed November 3, 1931. In Germany November 13, 1925 16 Claims. (Cl. 179-171) My invention relates to a connection for the rent with superimposed alternating current. The operation of high-frequency amplification sysdirect current is blocked by the condenser 7 and terns for receiving electric waves, and it is an flows exclusively in the resistance 6 and the bat- 7 object of my invention to eliminate the obnoxious tery 4. The alternating current, on the other tendency of the valve amplifiers to become selihand, is branched at 13, and its partial intensities 69 excited. are inversely proportional to the resistances of To this end, I arrange intermediate the anode the branches 6, 4 and '7, 8, with consideration of and the cathode of a valve a series unit comprisphase distortion, if any. ing a capacity and a self-inductance which unit When the series unit is tuned to the operating is tuned to the operating frequency of the sysfrequency it constitutes apurely ohmic resistance, 65 tem and the voltage induced in this unit will the total resistance between its ends being a be a maximum when the voltage in the valve minimum as the apparent impedance is zero. may be a minimum. The induced voltage is With the series unit tuned, especially if the ohmic transmitted to the grid of the following valve series resistance 6 is high in proportion to the through galvanic, capacitative or inductive couohmic resistance of the series unit, the anode 70 pling, and, if desired, may be transformed upalternating current will flow principally in the ward before being thus transmitted. unit and under these conditions the alternating The undesirable self-induction of the valves is voltage at the ends of the coil 8 will be a maxidue to a comparatively high voltage between the mum and equal to I w L. At the same time,

anode and the cathode of the valve which acts on the alternating voltage between the anode and 75 the grid past the capacity intermediate the anode the cathode of the valve 3 is a minimum and is and the grid so that undesired back-coupling and only determined by the value of the ohmic resistoscillations are generated. ance in the series unit.

This maybe counteracted by the known neutro- If the size of the self-inductance 8 were indyne connection by which the back-coupling efcreased and that of the condenser '7 were reduced 80 fect of the voltage between the anode and the in order to maintain the tuned condition of the cathode of the valve is balanced, but in my invensystem, the voltage at the ends of the self -induction the voltage is not balanced but eliminated. tance 8 would increase unless accidentally the In the draw three d agrams of connections ohmic resistance of the self-inductance 8 had inaccording to my ve t a e u a d y Way creased with its increase in size. The increase of 85 of example. the voltage may be prevented in practice with- F 1 is a diagram 0f i out difficulty. If the ohmic resistance of the 2 is Similar diagram Showing a b c series unit is small enough and consequently the Coupling in Series With the Series unitvoltage between the cathode and the anode of the Referring HOW to 1, 1 is an antenna, 2 is valve 3 is small, the tendency of undesired back- 90 a tunable g d i 3 is a high-frequency Valve coupling and of self-oscillation of the valve 3 is amplifier in the grid circuit 2 of which voltage 1 u ith th waves employed. is induced by the antenna 1, 4 is an anode bat- The connection illustrated permits the transtery, 5 is a radio frequency y-p s ondenser formation of an alternating voltage between the connected in parallel to said battery, 6 is an anode and the cathode of a valve by other means. 95 ohmic series resistance past which the battery than those hitherto employed and the operation 4 is connected with the anode circuit 3 at 14. will be similar to that of aresonance transformer.

7 is a rotating plate condenser, 8 is a self-in- A current self-inductance which might inductance, 9 is a battery supplying the grid voltcrease the voltage between the anode and the age for the following valve 3', and 10 is a radio cathode of the valve, is not shown in Fig. 1. If it 100 frequency by-pass condenser in parallel to the were provided and the coupling from the self-inbattery. The parts 7 and 10 constitute the series ductance 8 to the grid of the following valve 3' unit which is connected to the grid circuit of were suitably modified, for instance inductive, the the valve 3 at 11 and 12. current self-inductance might be balanced by When the valve 3 is excited by the antenna 1 the condenser 7. 105 and the tuned grid circuit 2, alternating voltage The curve indicating the voltage at the ends of will form at the ends of the self-inductance 8, the self-inductance 8 as determined by the adsince the condenser 10 is without influence in justing of the condenser 7 is very similar to a, this respect, intermediate the points 11 and 12. resonance curve the width of which is deter- The anode current of the valve 3 is direct curmined by the proportion of the resistance of th 11 series unit to the value of the resistance in the circuit 5, 6.

The voltage at the points 11, 12 is transmitted to the following valve 3 which, as shown, may be a directive valve amplifier. Obviously, another high-frequency valve might be provided in its stead, or a plurality of such valves might be provided, with a directive amplifier or an audion at the end of the line.

The operation as described will be performed so long as only voltage, and not power, is transmitted at 11, 12. If power were transmitted, ohmic resistance would be impressed on the series unit at '7, S, and this would be wrong in principle. But, on the one hand, power can only be transmitted from the anode circuit of a valve if the voltage between the anode and the cathode were greater than corresponds to the ohmic resistance of the series unit at '7, 8 for the power transmitted is invariably equal to the square of the anode current multiplied with the effective resistance transmitted to the anode circuit of the valve, and the anode alternating voltage will obviously increase with this resistance. On the other hand, the connection illustrated prevents the formation of a higher alternating voltage than corresponds to the power transmitted, because stray self-inductance, that is, self-inductance transmitted to the anode circuit, or prevailing capacity, may be balanced by setting the condenser 7.

For receivers, the transmission of effective resistance to the anode circuit, as indicated above, is impossible because the grids of the following amplifier or directing valves which operate the negative range, are excited without power. The cause why the high-frequency valves of the connections as employed hitherto, had a tendency to self-exciting, was the formation of alternating voltage between the anode and the cathode of the valve which was not generated by transmitted effective resistance but was due to prevailing of the capacity or inductance of the anode circuit. This is very probable because the power which the grid of a following valve consumes, even if the valve is not in the negative range, is so small in proportion to the power transmitted from the preceding valve that the effective resistance would be only a very small percentage of the ohmic resistance in the anode circuit of the preceding valve. But in fact, as shown, the ohmic resistance is not the cause of too high alternating anode voltage in the preceding tube but the prevailing of inductance or capacity in the anode circuit.

With the connection illustrated in Fig. 1 backcoupling may be provided at the first valve as shown in Fig. 2. Referring now to that figure, 14 is a back-coupling coil in series with series unit comprising the self-inductance 8 and the condenser '7. The back-coupling is a definite and purely inductive one because the stray selfinduction transmitted to the anode circuit 2 and which might generate an additional inductive voltage, may be balanced by the condenser 7 of the series unit.

The system illustrated in Fig. 2 has the further good feature as compared with the usual systems that the maximum back-coupling voltage exists when the system 14, 7, 8 is tuned as in this case the maximum anode alternating current will occur in the branch 14, 7, 8.

It will be understood that my improved connection is equally applicable to senders and receivers and enables me to build receivers operating principally at high-frequencies, the high-frequency amplification being practicable to an extent not attained in the existing systems. Highfrequency is so desirable for receivers because it intensifies low-frequency interferences which often are troublesome, to a lesser degree than with low -frequency amplification. High-frequency amplification may be extended until it is possible to use telephones the operation of which is based on capaoitative action. This eliminates for instance receiver distortions which are brought about by the non-straight-line operation of the usual rectifiers, such as detectors and audions.

It should be noted that in the valves used in connection with my systems the steepness of the characteristic or mutual conductance is important for the degree of amplification. This is in contradistinction to the usual amplifier systems where the degree of amplification with adapted suitable outer resistance is only determined by the inverse or reciprocal amplification factor of the given valve. The feature that in the present case the degree of amplification is a function of the steepness of the characteristic or mutual conductance, is a particular advantage in that it is possible to obtain higher amplifications by increasing the steepness. As in the present instance the alternating voltages between the anodes and the cathodes of the valves are but small it is possible to use valves characterized by a high inverse-amplification factor which may be operated on the other hand at correspondingly low anode voltage.

I claim:

1. A connection for the operation of high frequency ampl fication systems, comprising, a plurality of valve amplifiers having a including capacity and self-inductance arranged in series intermediate the anode and cathode of one of said valves, said path including a feed-back coil and being series tuned to the operative frequency of the system, the coil being coupled to the input circuit of the said one valve and a conductive coupling means for transmitting the voltage in a portion of said path to the grid of another valve.

2. A connection for the operation of high frequency amplification systems, comprising, a plurality of valve amplifiers having a path including capacity and self-inductance arranged in series intermediate the anode and cathode of one of said valves, said path including a feed-back reactance external of said latter valve and being series tuned to the operative frequency of the system, said reactance being coupled to the input circuit of said one valve means for transmitting the voltage drop in the inductive portion of said path to the grid of another valve, a second path including a source of electrical energy and a high impedance connected in parallel to the cathode and the anode of said first mentioned valve,

3. A connection for the operation of high frequency amplification systems, comprising, a plurality of valve amplifiers havin a path including a variable capacity and a self-inductance arranged in series intermediate the anode and cathode of one of said valves, said path including a feed-back means independent of said latter valve and being series tuned to the operating frequency of the system, said means being coupled to the input circuit of said one valve, and means including a grid biasing source for transmitting the voltage drop in a portion of said path to the grid of another valve.

4. A connection for the operation of high frequency amplifier system, comprising, a plurality of valve amplifiers having a path including capacity and self-inductance arranged in series intermediate the anode and cathode of one of said valves, said path including a series feed-back coil and being series tuned to the operating frequency of the system, said coil being coupled to the input circuit of said one valve and means including a grid biasing source for transmitting the voltage in a portion of said path to the grid of another valve.

5. In combination, an electron emission tube. an anode circuit therefor having a branch, coupling means in said branch and a utilization circuit coupled thereto, said branch circuit including a feed-back means independent of the tube and being arranged to have substantially no impedance with respect to the tube at signal frequency whereby current fluctuations in said branch cause substantially no anode potential fluctuations of signal frequency said means being coupled to the input circuit of the tube.

6. In combination, an electron emission tube. an anode circuit therefor including a feed-back coil and being series resonant to the desired operating frequency, said coil being coupled to the input circuit of the tube, a source of anode potential, a circuit of low admittance to high frequency energy relative to said resonant circuit for applying energy from the source to the anode, means to utilize the tube output, and means coupling the utilization means to only a portion of the series resonant circuit.

'7. A connection for the operation of highfrequency amplification systems comprising a plurality of valve amplifiers, a series unit including a capacity and a self-inductance arranged intermediate the anode and the cathode of one of said valves and tuned to the operating frequency of the system, a coil in series with said unit and adapted to effect back-coupling with the grid circuit of said valve, and means for transmitting the voltage in said unit to the grid of another valve.

8. The method of preventing capacitive feed back in an electron emission tube circuit which includes the steps of resonating a portion of the anode circuit of the tube at a desired frequency which includes the steps of series resonating a portion of the anode circuit of the tube at a desired frequency whereby anode current fluctuations cause substantially no anode potential fluctuations at the resonant frequency at said portion, and feeding back energy from the anode circuit to the control electrode circuit of the tube through a path other than the inter-electrode capacities of the tube.

9. The method of coupling utilization means to the anode circuit of an electron emission tube for the prevention of capacitive feed back which includes coupling the utilization means to a reactance in the anode circuit and series resonating the reactance with another reactance at a desired frequency in order to reduce the potential fluctuations on the tube anode at the said frequency and feeding back energy from the anode circuit to the grid circuit of the tube through a path other than the tube inter-electrode capacities.

10. In combination, in a radio system, an electron emission tube having an anode circuit including a path containing capacity and selfinductance, said path being series tuned to the operating frequency of the system, means con nected to said path for feeding back energy to the grid circuit of said tube, and means for transmitting the voltage drop in a portion of said path to another valve.

11. In combination, an electron emission tube, an anode circuit therefor, and a series resonant path in said circuit so arranged that current fluctuations therein cause substantially no anode potential fluctuations of an operating frequency when said means is tuned to resonance to the operating frequency said path including means for feeding back energy to the grid circuit of the tube.

12. The method of preventing capacitive feed back in an electron emission tube circuit which consists in series resonating an external connection between the anode and cathode of the tube at signal frequency for causing anode current fluctuations in said connection at signal frequency without substantial anode potential fluctuation at said frequency, feeding back energy from the anode circuit to the grid circuit through a path other than the tube capacities, and simultaneously maintaining another portion of the anode circuit at a low admittance to high frequency energy.

13. In combination, in a radio receiver, a source of signal energy, a radio frequency amplifier tube including a tunable input circuit coupled to the source, a second radio frequency amplifier tube, an electrical reproducer connected in the output circuit of the second tube, and means, coupling the anode circuit of the first tube and the input circuit of the second tube, arranged to have substantially no impedance with respect to the first tube at signal frequency whereby current fluctuations in said coupling means cause substantially no anode potential fluctuations of signal frequency in the first tube.

14. In combination, in a radio receiver, a plurality of tuned radio frequency amplification stages in cascade, and an electrical reproducer connected directly in the output circuit of the last of said stages.

15. In combination, in a radio receiver, a plurality of tuned radio frequency amplification stages in cascade, and a capacitative reproducer stages in cascade, and an electrical reproducer connected directly in the output circuit of the last of said stages, each stage including a tube having a high mutual conductance.

WALTER scHAFFER.

CERTIFICATE OF CORRECTION.

?atent No. 1,956,964. May 1,1954.

WALTER soalirres.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, first column, line 42, for the numeral "14 read 15; and line 47, for "and" read to; and that the said Letters Patent should. be read. with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed. this 4th day of August, A. D. 1956.

Henry Van Arsdale (Seal) Acting Commissioner of Patents. 

